Exploring, drilling and completing hydrocarbon wells are generally complicated, time consuming and ultimately very expensive endeavors. As a result, over the years increased attention has been paid to monitoring and maintaining the health of such wells. Significant premiums are placed on maximizing the total hydrocarbon recovery, recovery rate, and extending the overall life of the well as much as possible. Thus, logging applications for monitoring of well conditions play a significant role in the life of the well. Similarly, significant importance is placed on well intervention applications, such as cleanout techniques which may be utilized to remove debris from the well so as to ensure unobstructed hydrocarbon recovery.
Cleanout techniques as indicated above may be employed for the removal of loose debris from within the well. However, in many cases, debris may be present within the well that is of a more challenging nature. For example, debris often accumulates within a well in the form of ‘scale’. As opposed to loose debris, scale is the buildup or caking of deposits at the surface of the well wall. The well wall may be a smooth steel casing within the well that is configured for the rapid uphole transfer of hydrocarbons and other fluids from a formation. However, a buildup of irregular occlusive scale may occur at the inner surface of the casing restricting flow therethrough. Scale may even form over perforations in the casing, thereby also hampering hydrocarbon flow into the main borehole of the well from the surrounding formation. Furthermore, scale buildup often occurs at shut-off safety valves, gas lift mandrels, and other completion assemblies. In addition to the occlusive nature of the scale, this particular type of buildup has the added disadvantage of interfering with the functionality of such features.
In order to address scale buildup as noted above, a variety of conventional techniques are available. Often times a less expensive gravity fed wireline technique is employed wherein chemical cleaners such as hydrochloric acid are delivered to downhole sites of scale buildup. More particularly, bailers disposed at the end of a wireline are filled with a chemical cleaning mix which is dumped on the scale buildup downhole. Unfortunately, scale buildup is generally resistant to passively delivered conventionally available chemical mix suitable for downhole use. For example, it is unlikely that calcium carbonate, barium sulfate and other crystalline scale deposits will be adequately removed by such techniques. Therefore, more extensive mechanically invasive cleanout as described below is generally required.
Scale may be removed by a variety of mechanical techniques such as the use of explosive percussion, impact bits, and milling. However, these techniques include the drawback of potentially damaging the well itself. Furthermore, the use of impact bits and milling generally fails to remove scale in its entirety. Rather, a small layer of scale is generally left behind which may act as a seed layer in encouraging new scale growth. As a result of these drawbacks, mechanical fluid jetting tools as described below may be most often employed for scale removal.
Fluid jetting tools are often deployed within a well to remove scale buildup as described above. A jetting tool may be conveyed into the well via coiled tubing and include a rotating head for jetting pressurized fluids, chemicals, solutions, beads, particles, penetrants toward the well wall in order to fracture and dislodge the scale. The rotating head may include fluid dispensing arms that project outward from a central axis of the tool and toward the well wall. Additionally, in many cases, the water may include a chemical mix or an abrasive in order to aid in the cutting into and fracturing of the scale as indicated.
The above noted jetting tools are delivered downhole to the site of the cleanout by way of coiled tubing. Unfortunately, in order for the application to take place, the well must be shut down and coiled tubing equipment, having a massive “footprint”, must be delivered to the oilfield. For example, the coiled tubing, having a jetting tool at a downhole end thereof, may be driven through the well to the site of the cleanout through injector equipment. Additionally, a series of pumps, prime movers and control equipment may also be delivered to the oilfield in order to direct the coiled tubing cleanout application. As a result, several thousands of dollars more may be spent in running the coiled tubing cleanout application as compared to the above noted wireline cleanout.
Unfortunately, as indicated above, while more cost-effective, the more minimal wireline cleanout application remains largely ineffective at actually removing scale. Alternatively, while generally effective in achieving scale removal, the indicated coiled tubing cleanout techniques involve expenses that are so exorbitant, older scale ridden wells are often simply shut down rather than facing the prospect of running a coiled tubing cleanout application on them.